Field of the Invention
The invention pertains to the field of electric phasers (e-phasers). More particularly, the invention pertains to an electric phaser with an anti-backlash planetary drive.
Description of Related Art
In a closed loop power transmission system, variable cam timing (VCT) is the system that measures the angular displacement, or phase angle, of a camshaft, relative to the crankshaft to which it is operatively connected and then alters the phase angle to adjust various engine characteristics in response to demands for either an increase or a reduction in power. Typically, there is a feedback loop in which the desired values of such engine characteristics are measured against their existing values, and changes are effected inside the engine in response to any variances. To accomplish this, modern automobiles usually have one or more Electronic Control Units (ECU), which constantly analyze data fed into them from various parts of the engine or from other parts of the automobile, such as, for example, exhaust gas sensors, pressure sensors, and temperature sensors. A control signal is then emitted in response to such data. For example, with regard to VCT systems, as changes occur in engine or external conditions, the angular displacement between the camshaft and the crankshaft is adjusted accordingly.
A VCT system includes a cam phasing control device, sometimes referred to as a phaser and may include, control valves, control valve actuators, and control circuitry. VCT is a process that refers to controlling and varying, when desirable, the angular relationship (the “phase”) between the drive shaft and one or more camshafts, which control the engine's intake and exhaust valves. An electric phaser (e-phaser) is driven by an electric motor to control and vary the angular relationship between the drive shaft and one or more camshafts. In response to input signals, the electric phaser adjusts the camshaft to either advance or retard engine timing.
U.S. Patent Application Publication No. 2007/0179011, by Choi et al., entitled “Variable Gear Ratio Steering Apparatus for Automobiles” and published Aug. 2, 2007, discloses a variable gear ratio steering apparatus including an input shaft connected to a steering wheel, a sun gear coaxially formed with the input shaft while enclosing the input shaft, a first pair of planet gears externally meshing with the sun gear, a second pair of planet gears externally meshing with the sun gear, a first carrier coupled to the input shaft while connecting the first pair of planet gears, a second carrier adapted to rotate relative to the input shaft while connecting the second pair of planet gears, a ring gear internally meshing with the first and second pairs of planet gears, and an input shaft connected to the ring gear. The second carrier is inserted into the first carrier while being supported by a compression means so that the second carrier can rotate relative to the input shaft to reduce backlash.
WO 2014/092963, by Showalter, entitled “Split Ring Gear Planetary Cam Phaser” and published Jun. 19, 2014, discloses a cam phaser for dynamically adjusting a rotational relationship of a camshaft of an internal combustion engine with respect to an engine crankshaft. The cam phaser can include a planetary gear system having a split ring gear, including a sprocket ring gear to be driven by the engine crankshaft through an endless loop power transmission member and a camshaft ring gear connectable for rotation with the camshaft. A sun gear can be located concentric with the split ring gear, and a number of planet gears can be in meshing engagement between the sun gear and the split ring gear. The camshaft ring gear can have a different number of teeth, greater or lesser, than the sprocket ring gear by a value corresponding to a multiple of the number of planet gears to provide tooth alignment at an engagement position of each of the planet gears.